Typical magnetic bit holders include a cylindrical body having a socket formed axially in one end configured to receive one of a plurality of interchangeable bits. The socket of the bit holder typically has a transverse cross-sectional shape which is non-circular, such as polygonal. The proximal end of the bit has a complementary shape that fits in the socket. A permanent magnet is typically press-fitted or crimped into a hole at the base of the socket to magnetically retain the associated bit in place.
For many applications, however, the location of fasteners prevents the user from directly aligning the bit holder with the fastener. This limitation impedes the ability of the user to apply maximum torque to the fastener, and increases wear on both the fastener and the interchangeable bit. In order to overcome this problem, hand tools have been designed that have working ends displaceable or pivotable away from the longitudinal axis of the shank of the tool.
U.S. Pat. No. 2,773,529 (Valenti) discloses a screwdriver having a pivotable tool bit part which allows it to be pivoted to a right angle to the screwdriver shank by the rotation of a clamp member which manually holds the tool bit part in alignment with the shank.
U.S. Pat. No. 4,271,731 (Suligoy et al.) discloses a socket member pivotally attached to a shaft by means of pivot pins. The socket member includes a socket cavity having a conventional polygonal or ribbed cross-section to receive the correspondingly cross-sectioned shank end of a bit. In one embodiment, an elongated collar is provided to retain the socket member in axial alignment with the shaft.
U.S. Pat. Nos. 4,711,145 (Inoue); 5,042,332 (Nickipuck); and 5,577,426 (Eggert et al.) each teach fastener-driver constructions having an angularly-displaceable component.
These embodiments, however, locate the pivot point of the bit relative to the bit holder too far behind the working end of the bit. The misalignment requires eccentric rotation of the bit, resulting in excessive wear on both the working end of the bit and the fastener.
U.S. Pat. No. 2,667,194 (Fisher et al.) discloses interchangeable bits that are retained in the bit holder by a snap ring. The square bit receiving socket has a somewhat larger cross section than the square portion of the bit. The resulting clearance permits the bit to “float” in the socket so that the components may be out of axial alignment and still provide proper driving of the bit and proper fit of the bit point with the screw. Fisher discloses clearances in the range of about 0.005 inches to about 0.010 inches, corresponding to an angular displacement of the bit in the socket of less than about 3 degrees. Large axial forces along the longitudinal axis of the bit and the bit holder drive the flat end of the bit into the base of the receiving socket, inhibiting angular displacement.